Government and commercial buildings (e.g., embassies, court houses, hotels, casinos, malls, airports and stadiums) have proven attractive targets for bombing attacks throughout the world in recent years. The attacker, in most cases, is a politically motivated terrorist using, as a weapon, a high explosive device transported and detonated inside a vehicle nearby the targeted building. The explosive device carried in such vehicles is typically capable of generating a shock wave of sufficient force as to shear the face off unprotected buildings, leading to tremendous loss of life and property damage. The resulting debris field surrounding the building is often several feet thick blocking entrances. In addition, glass remnants dangle precariously, potentially falling from great heights to the ground in the slightest breeze. Consequently, both hazards hinder and threaten the safety of emergency response teams as they attempt to enter the damaged building to render aid to the injured.
The simplicity and stealth of vehicular weapons make them a complex foe. It is virtually impossible to screen all the cars and trucks that rumble past critical buildings. Defending against such an explosive device involves keeping vehicles at a distance from vulnerable targets, often using Jersey barriers, blocks, bollards and other concrete structures (See e.g., U.S. Pat. Nos. 7,144,186 and 6,767,158, and U.S. Published Patent Application No. 2004/0261332). However, this can be difficult where public roads pass immediately outside these structures. Closure of roads, or protecting buildings with concrete barriers is not always practical, as it can often be unsightly and is therefore generally undesirable.
Existing buildings rarely have blast resistant construction and thus much emphasis has been placed on retrofits for windows to mitigate glass hazards. The use of so-called safety glazing or penetration-resistant glazing for windows, using multiple layers of polycarbonate, glass, and other resinous materials is well known. For example, glass-polycarbonate resin laminates adhering together with ethylene-vinyl copolymers are described in U.S. Pat. No. 3,666,614. In U.S. Pat. No. 3,520,768, there are described laminates of relatively thick glass having a comparatively thin polycarbonate foil as the adhering material. U.S. Pat. No. 3,624,238 concerns a bullet resistant laminated structure that includes outer faces or plies of safety glass with an intermediary ply formed of a polycarbonate resin.
U.S. Pat. No. 6,266,926 describes a flexible apparatus that is deployed by inflating a protective barrier adjacent to windows to reduce the quantity of debris hazard in the event of an explosion. U.S. Pat. No. 6,349,505 discloses a louver system mounted adjacent to the inside and/or outside of a glass window and reinforced using high elongation cables or straps attached to the floor and ceiling. The louver system would immediately close upon detection of an explosion, reducing the quantity of debris hazard in the building.
U.S. Pat. No. 4,625,659 discloses a bullet and explosion proof window or door system comprising two spaced apart panels, whereby the outer panel is spaced from a support soffit such that a gap is formed for providing a ventilation channel. However, peripheral portions of the panels are fitted with a security layer in order to prevent projectiles from entering through the ventilation gap. U.S. Pat. Nos. 6,177,368 and 4,642,255 discloses blast-resistant panels produced from PVC and woven fiberglass, and polyvinyl acetal, glass and a fibrous layer encapsulated in the polyvinyl acetal layer. U.S. Pat. No. 3,191,728 discloses a barrier consisting of welded metal strips, as protection for workers in aircraft parking areas from the exhaust of jet engines.
U.S. Published Patent Application No. 2007/0011962 discloses a transparent assembly locatable in a building surface having a rebate. The assembly has a transparent panel and one or more high tensile strength flexible material reinforcement pieces extending laterally from the panel to provide non-rigid attachment of the assembly to a subframe and/or wall. The attachment is said to allow movement of the assembly within the rebate. By direct but non-rigid attachment of the transparent assembly, generally a window, to the subframe and/or wall, any weakness in the impact-resistance of the assembly because of weakness and/or damage to the frame is said to be avoided. The non-rigid nature of the attachment is said to allow it to absorb much of the blast loading which in turn is said to allow a large load on the transparent assembly to be supported by the subframe and/or wall.
A self-centering energy dissipative brace apparatus with tensioning elements is described in U.S. Published Patent Application No. 2008/0016794.
U.S. Published Patent Application No. 2004/0226231 provides a blast resistant assembly for use as a window, door, or the like, that is capable of withstanding a bomb blast, hurricane, tornado, or other strong force. The assembly includes a composite panel that comprises a glass sheet bonded to a polymeric layer, and a frame that surrounds the composite panel. In the event of an explosion or other strong force, the composite panel is secured within the frame by one or more retainers. Each retainer includes an extension that is embedded within the polymeric layer. The composite panel may also be pivotally mounted to the frame to facilitate deflection of the composite panel during a blast, and to provide a means for emergency exit.
In U.S. patent application Ser. No. 11/983,980, the present inventors present a blast-resistant barrier comprising a plurality of units each including a panel having a thickness of greater than 20 to less than 40 millimeter. The panel is in the form of a monolithic polycarbonate sheet or a laminate positioned vertically between the source of a blast and the blast target, the laminate including at least two polycarbonate sheets and an optional image layer interposed therebetween. The panel is fixedly attached to a frame which is firmly embedded in concrete in a manner calculated to provide stiffness sufficient to absorb and withstand external forces resulting from the blast.
Retrofits to protect building facades have traditionally involved strengthening of walls. To be truly effective, wall-strengthening is often an invasive operation which adversely affects the appearance of the structure and impacts building operations. It is, therefore, desirable to have a structure that is unobtrusive, easy to install, and at the same time protective of the entire building from the devastating effects of a vehicular bombing attack.